/* Reference_IDCT.c, Inverse Discrete Fourier Transform, double precision          */



/* Copyright (C) 1996, MPEG Software Simulation Group. All Rights Reserved. */



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 * The MPEG Software Simulation Group does not represent or warrant that the

 * programs furnished hereunder are free of infringement of any third-party

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/*  Perform IEEE 1180 reference (64-bit floating point, separable 8x1

 *  direct matrix multiply) Inverse Discrete Cosine Transform

*/





/* Here we use math.h to generate constants.  Compiler results may

   vary a little */



#include <math.h>



#include "config.h"



#ifndef PI

# ifdef M_PI

#  define PI M_PI

# else

#  define PI 3.14159265358979323846

# endif

#endif



/* global declarations */

void Initialize_Fast_IDCTref _ANSI_ARGS_((void));

void Reference_IDCT _ANSI_ARGS_((short *block));



/* private data */



/* cosine transform matrix for 8x1 IDCT */

static double c[8][8];



/* initialize DCT coefficient matrix */



void Initialize_Reference_IDCT()

{

  int freq, time;

  double scale;



  for (freq=0; freq < 8; freq++)

  {

    scale = (freq == 0) ? sqrt(0.125) : 0.5;

    for (time=0; time<8; time++)

      c[freq][time] = scale*cos((PI/8.0)*freq*(time + 0.5));

  }

}



/* perform IDCT matrix multiply for 8x8 coefficient block */



void Reference_IDCT(block)

short *block;

{

  int i, j, k, v;

  double partial_product;

  double tmp[64];



  for (i=0; i<8; i++)

    for (j=0; j<8; j++)

    {

      partial_product = 0.0;



      for (k=0; k<8; k++)

        partial_product+= c[k][j]*block[8*i+k];



      tmp[8*i+j] = partial_product;

    }



  /* Transpose operation is integrated into address mapping by switching 

     loop order of i and j */



  for (j=0; j<8; j++)

    for (i=0; i<8; i++)

    {

      partial_product = 0.0;



      for (k=0; k<8; k++)

        partial_product+= c[k][i]*tmp[8*k+j];



      v = (int) floor(partial_product+0.5);

      block[8*i+j] = (v<-256) ? -256 : ((v>255) ? 255 : v);

    }

}

